Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Semiconductor devices perform a wide range of functions such as analog and digital signal processing, sensors, transmitting and receiving electromagnetic signals, controlling electronic devices, power management, and audio/video signal processing. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, diodes, rectifiers, thyristors, and power metal-oxide-semiconductor field-effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, application specific integrated circuits (ASIC), standard logic, amplifiers, clock management, memory, interface circuits, and various signal processing circuits.
An image sensor is a type of semiconductor device that detects and records an image by converting the variable attenuation of light waves or electromagnetic radiation into electric signals. An image sensor can be implemented with semiconductor charge-coupled devices (CCD) and active pixel sensors in complementary metal-oxide-semiconductor (CMOS) or N-type metal-oxide-semiconductor (NMOS) technologies with applications in digital cameras, video recorders, medical imaging equipment, night vision equipment, thermal imaging devices, radar, sonar, and other image detecting devices.
The light source is typically focused onto a flat or planar image sensor surface through one or more optical lenses, e.g., up to four lenses. The optical focusing lenses add cost, complexity, and height to the semiconductor package. Even with optical lenses, the focus is often better in the center region and less on the edges of the image sensor. Image sensors are continually driving towards higher resolution, faster focus times, better focus depth, lower profile, and lower cost.
One approach to reducing the number of optical focusing lenses or eliminating the need for optical lenses is to make the image sensor with a curved surface. FIG. 1a shows a known image sensor die 50 with active imaging surface 52 disposed over substrate 54 having a curved surface 56. Image sensor die 50 is attached to curved surface 56 of substrate 54 with an epoxy. Image sensor die 50 conforms to curved surface 56 with application of pressure and heat. The epoxy is cured under pressure leaving image sensor die 50 molded to surface 56 a curved form factor, as shown in FIG. 1b. Image sensor die 50 in FIG. 1b is difficult to manufacture in high volume due in part to the curved nature of substrate 54, the curing process under pressure for the epoxy, the need to angle interconnecting bond wires, and lack of economies of scale. The process of FIGS. 1a-1b is high cost and not amenable with batch processing or mass production.